1. Field of the Invention
The present invention relates to a method of metallizing the surface of a ceramic material through electroless plating, and more particularly, it relates to an improvement in a pretreatment process previous to metallization.
2. Description of the Prior Art
In order to provide electrodes on a ceramic electronic component, the surface of the ceramic material is metallized through electroless plating as disclosed in U.S. Pat. Nos. 4,328,048, 4,402,494 and 4,464,422, for example. In advance of such metallization, the ceramic surface is generally etched so that a metal thin film is uniformly and strongly adhered to the ceramic surface. In general, such etching is chemically performed through an aqueous solution of nitric acid, sulfuric acid, hydrofluoric acid or the like.
In another conventional method of metallizing a ceramic material, an activating paste containing a metallic salt of Pd or the like is coated on the ceramic surface and baked, and then subjected to electroless plating.
However, when pretreatment is performed through the strong acid in the first mentioned conventional method of metallizing a ceramic material, vapor containing the strong acid tends to gather in the circumference with increase in concentration of the strong acid, thereby causing corrosion of peripheral apparatuses and environmental pollution. Further, ceramic material is not easily etched even if strong acid of high concentration is employed, and hence the etching process must be performed at a high temperature for a long time.
Such problems are particularly serious in metallization of etching-resistant ceramic materials such as ZrO.sub.2 -TiO.sub.2 -SnO.sub.2 ceramics.
In the case of the last-mentioned conventional method, a coaxial type ceramic material structure, employed in a dielectric resonator for example, is so complicated in configuration that coating of the paste is difficult, leading to uneven coating and increase in the working time.